In the wafer-sort stage of the manufacturing of semiconductor devices, devices are tested while still in wafer form. In this stage a critical component called a probe card is used. The probe card interfaces a tester to the semiconductor device.
The probe card, depicted in FIG. 1, typically consists of a printed circuit board with probe pins mounted in an epoxy ring, configured such that the tester can be connected to the probe card and have continuity to pads on the semiconductor device via the probe pins touching the pads. The probe pins are generally made of hard, thin, tapered wire, each bent specifically to contact just one pad without contacting neighboring pins or pads.
Because the semiconductor device under test is typically very small, the probe pins are correspondingly small and very close together. In the present application, a typical probe pin diameter might be 1.5 mils at the tip, tapered to 10 mils at the base, and a pad can be 2-4 mils wide, 1-2 mils between it and the next pad. Generally, dozens of pins are required to access all pads on a device. In order for the probe card to properly contact the pads, the tips should be positioned within a 1 mil range in planarity (vertical or z positioning, perpendicular to the card) and 0.1 mil in alignment (horizontal or x-y positioning). 1 mil planarity means that as the probe pins descend on the pads, all tips must contact the pads within 1 mil of descent from the point that a first tip contacts a pad. 0.1 mil alignment means that each probe tip must contact its pad in the center, not varying more than 0.1 mil in any direction. The scale of this can be appreciated when one realizes that a human hair is roughly 4 mils wide (see FIGS. 1 and 2).
Aligning these pins to such tolerances is challenging because they are so small and because they are generally made of a hard material such as tungsten. A probe card is mounted underneath a microscope and each pin is individually, manually worked until it comes within tolerance. This process can take hours.
Precision manipulating hand tools are not available for this work, so the technician constructs his own by bending a sharp tweezer tip into a tiny hook. The hook is then used to pull and stroke the pin this way or that, until the pin is bent to proper alignment. A disadvantage to the hook is that it does not push very well, which can make the process awkward.